MySQL Router failing with “write error: Resource Temporarily Unavailable”

Question

I have been using MySQL Router for the past few months without any issues, but I just ran apt-get upgrade on my Linux server, and mysql-router was upgraded from version 8.0.21 up to 8.0.22.

Since then, my connections are hanging when I try to pull back more than about 50 rows of data.

When I look in the mysqlrouter.log file, it show a series of DEBUG messages like this:

2020-10-30 12:55:14 routing DEBUG [7f259745a700] fd=12 write error: Resource temporarily unavailable

Incidentally, I have now uninstalled and re-installed the previous version and it's working as expected.